The present invention relates to an alignment device for a vehicle, and particularly to an alignment device for a vehicle suitable to align an optical axis of a headlamp for an automobile.
In some vehicles such as an automobile or the like, an alignment device (auto leveling device) is mounted to prevent the direction of irradiation of light of a headlamp from becoming irregular due to changes in the running attitude of the vehicle. The alignment device corrects the direction of light irradiated by the headlamp according to the changes in the running attitude of the vehicle. For example, vehicle height sensors arranged at axle portions in the front and in the rear of the vehicle generate detection signals that correspond to the change of a pitting angle (or pitch angle) of the vehicle, and the direction of light irradiated by the headlamp is controlled according to this change.
Specifically, the alignment device shown in FIG. 4 includes a vehicle height sensor 50, a control unit 52 and an actuator 54. Electric power is supplied to the control unit 52 and the actuator 54 from a vehicle power supply. The control unit 52 includes a controller 62 comprising resistances 56 and 58, a stabilized power supply 60 and a microcomputer, and a D/A converter 64. The stabilized power supply 60 stabilizes voltage upon reception of a supply of the electric power from the vehicle power supply, and outputs the stabilized voltage to the controller 62 and to the D/A converter 64. The controller 62 receives the voltage divided by the resistances 56 and 58 therein, monitors the voltage change of the vehicle power supply in accordance with this voltage, converts a detection signal of the vehicle height sensor 50 to a digital signal, performs an alignment operation, for example, alignment according to the change of the pitting angle of the vehicle on the basis of the digital signal, and outputs a digital signal in accordance with this operation result to the D/A converter 64. The D/A converter 64 converts the digital signal from the controller 62 to an analog signal and outputs this analog signal to a motor driver 66 of the actuator 54.
The motor driver 66 compares the analog signal output from the D/A converter 64 with the rotational position of a motor detected by a potentiometer 68, and drives a motor 70 according to the result of the comparison. Consequently, the motor driver 66 drives the motor 70 so that the output signal of the D/A converter 66 conforms to the position detected by the potentiometer 68. The motor 70 tilts a reflector within a lamp body up and down, so that the optical axis of the lamp is aligned according to the change of the vehicle height.
In the conventional alignment device, a constant voltage is always supplied to the controller 62 by the stabilized power supply 60. Therefore, even if the voltage of the vehicle power supply varies, no error is produced in the operation result of the controller 62. However, since the vehicle power supply is directly supplied to the motor driver 66 and potentiometer 68 in the actuator 54, the detection value of the potentiometer 68 is under the influence of variations of the supply voltage. The conventional alignment device includes a voltage divided by the resistances 56 and 58 that is input to the controller 62, and thus the controller 62 monitors the voltage variation of the vehicle power supply and corrects the operation value according to the variation of the supply voltage. Therefore, in the conventional alignment device, in order to monitor the variation of the supply voltage. the resistances 56 and 58 must be provided to serve in a supply voltage monitor circuit so that the controller 52 can perform the correction operation.
Further, referring to FIG. 5, the D/A converter 64 of the conventional alignment device is composed of a rudder circuit 72 comprising a plurality of resistance elements and an operation amplifying circuit 74. Consequently, the number of parts is increased and the positional accuracy of the actuator 54 is decreased by the supply voltage.
For example, in case that the supply voltage of the controller 62 is 5V, the D/A converter 64 performs a digital/analog conversion on the basis of 5V. Conversely, since the actuator 54 operates at the voltage (battery voltage) of the vehicle power supply, an operational amplifier 74 is required, which converts the analog voltage which is 5V at its maximum into the highest value of the operation voltage in the system. Such circuitry is required because, if the actuator 54 is designed to operate at 5V, the motor 70 would have to be large which is not practical. When the stroke of the actuator 54 is 0, in the case that the operational voltage range of the system is 8V to 16V in order to output a signal corresponding to the battery voltage from the D/A converter 64, the gain of the operational amplifier 74 is 3.2 times. Since the actuator 54 operates on the basis of the battery voltage, and the amplification factor of the operational amplifier 74 is fixed, when the battery voltage is 8V, which is the lowest in the system operational voltage range, the digital value when the stroke of the actuator 54 is 0 must be half as large as one when the supply voltage is 16V. If not half, the output voltage of the D/A converter 64 does not approach that of the battery voltage. Accordingly, in case that a D/A converter of 8 bits resolution is used, the output voltage can be naturally adjusted at 256 gradations. However, the output voltage can be changed only by 128 gradations which is half of 256 gradations, so that the positional accuracy of the actuator 54 is lowered by half.
The invention has been made in view of the problem of the above prior art. In particular, presented is an alignment device for a vehicle which can align an optical axis of a light source according to the change of attitude of a vehicle without lowering the positional accuracy, and the alignment device offers a simple construction.
In order to achieve the above result, the alignment device for a vehicle according to the first aspect of the invention is designed to include a vehicle attitude detecting means for detecting an attitude of a vehicle and then outputting a vehicle attitude detecting signal of analog amount; an analog-to-digital conversion means for converting the vehicle attitude detecting signal to a digital signal; an operation means for executing alignment operation in accordance with the digital signal and outputting an alignment command signal of which the pulse duration has been modulated according to this operation result; a switching means which responds to the alignment command signal upon reception of electric power from a vehicle power supply to perform a switching operation and outputs a signal according to this switching operation; a filter means for smoothing the signal accompanying the switching operation of this switching means; an alignment means for aligning an optical axis in response to an alignment signal; a position detecting means for detecting the position of the optical axis upon reception of supply of the electric power from the vehicle power supply; and an alignment signal generating means which generates an alignment signal corresponding to the deviation between the output signal of the filter means and the detection output of the position detecting means and outputs it to the alignment means.
In a process in which the switching means performs the switching operation in response to the alignment command signal of which pulse duration has been modulated and the signal accompanying the switching operation of this switching means is smoothed by the filter means, when the supply voltage of the vehicle power supply varies, the signal accompanying the switching operation is smoothed in accordance with the variation of this supply voltage, and the variation of the supply voltage is absorbed by the smoothed signal. Therefore, by generating the alignment signal corresponding to the deviation between the output signal of the filter means and the detection output of the position detecting means, it is possible to prevent a reduction in the positional accuracy of the optical axis and it is also possible to reduce the number of the parts since it is not necessary to monitor the variation of the supply voltage of the vehicle power supply.
The alignment device for a vehicle according to the second aspect of the invention is designed to include a vehicle height detecting means for detecting the vehicle height and outputting an analog vehicle height detecting signal; an analog-to-digital conversion means for converting the vehicle height detecting signal to a digital signal; an operation means for executing an alignment operation in accordance with the digital signal and outputting an alignment command signal having a pulse duration that has been modulated according to this operation result; a switching means which responds to the alignment command signal upon reception of electric power from a vehicle power supply to perform a switching operation and outputs a signal according to this switching operation; a filter means for smoothing the signal accompanying the switching operation of the switching means; an alignment means for aligning an optical axis in response to an alignment signal; position detecting means for detecting the position of the optical axis upon reception of the electric power from the vehicle power supply; and an alignment signal generating means which generates an alignment signal corresponding to the deviation between the output signal of the filter means and the detection output of the position detecting means and outputs it to the alignment means.
In the process in which the switching means performs the switching operation in response to the alignment command signal having a modulated pulse duration and the signal accompanying the switching operation of this switching means is smoothed by the filter means, when the supply voltage of the vehicle power supply varies, the signal accompanying the switching operation is smoothed in accordance with the variation of the supply voltage, and the variation of the supply voltage is absorbed by the smoothed signal. Therefore, by generating the alignment signal corresponding to the deviation between the output signal of the filter means and the detection output of the position detecting means, it is possible to prevent a reduction in the positional accuracy of the optical axis and it is also possible to reduce the number of parts since it is not necessary to monitor the variation of the supply voltage of the vehicle power supply.
The alignment device for a vehicle according to the third aspect of the invention is, in the alignment device for vehicle according to the first or second aspect of the invention, so designed that the filter means includes a charge and discharge circuit for charging and discharging an electric current from the vehicle power supply according to the switching operation of the switching means. The time constant of this charge and discharge circuit is set to be faster than a response speed of the alignment means which responds to the alignment signal.
In the case where the time constant of the charge and discharge circuit is faster than the response speed of the alignment means, the alignment means does not repeat an on/off operation many times due to the alignment signal but the optical axis of the lamp can still be quickly aligned in the target position.
Examples for carrying out the invention will be described below with reference to an embodiment.